Gas supply system, substrate processing apparatus and gas
supply method

ABSTRACT

Prior to wafer processing, pressure ratio control is executed on a divided flow rate adjustment means so as to adjust the flow rates of divided flows to achieve a target pressure ratio with regard to the pressures in the individual branch passages. As the processing gas from a processing gas supply means is diverted into first and second branch pipings under the pressure ratio control and the pressures in the branch passages then stabilize, the control on the divided flow rate adjustment means is switched to steady pressure control for adjusting the flow rates of the divided flows so as to hold the pressure in the first branch passage at the level achieved in the stable pressure condition. Only after the control is switched to the steady pressure control, an additional gas is delivered into the second branch passage via an additional gas supply means.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of, and claims the benefitof priority under 35 U.S.C. §120 from, U.S. application Ser. No.13/524,613, filed Jun. 15, 2012, which is a divisional of U.S. Pat. No.8,221,638, issued Jul. 17, 2012; which is a divisional of U.S.application Ser. No. 11/615,062, filed Dec. 22, 2006 claims the benefitof priority under 35 U.S.C. §119 from Japanese Patent Application Number2006-000241, filed on Jan. 4, 2006 and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Provisional Application No. 60/773,676,filed Feb. 16, 2006. The entire contents of each of the aboveapplications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a gas supply system that supplies gasinto a processing chamber, a substrate processing apparatus and a gassupply method.

BACKGROUND OF THE INVENTION

In a substrate processing apparatus used in fields of applicationpertaining to the present invention, a specific type of processing suchas film formation or etching is executed on a target substrate toundergo processing (hereafter simply referred to as a substrate), whichmay be a semiconductor wafer or a liquid crystal substrate, by using aspecific gas supplied into a processing chamber.

Such a substrate processing apparatus may be, for instance, a plasmaprocessing apparatus. The plasma processing apparatus may include alower electrode also used as a stage on which a substrate is placed andan upper electrode also used as a showerhead through which the gas isinjected toward the substrate, both disposed within the processingchamber. In a plane parallel plate type plasma processing apparatus suchas this, plasma is generated by applying high-frequency power to thespace between the two electrodes while supplying the specific gas ontothe substrate placed inside the processing chamber through theshowerhead and the specific type of processing such as film formation oretching is executed with the plasma thus generated.

It has been a matter of crucial importance in the related art to improvethe planar uniformity achieved through the specific substrateprocessing, such as film formation or etching executed on the substrateby assuring consistent substrate surface processing characteristics suchas the etching rate, etching selection ratio, the film formation rate orthe like.

Japanese Laid Open Patent Publication No. H08-158072 (patent referenceliteratures 1) and Japanese Laid Open Patent Publication No. H09-045624(patent reference literatures 2), for instance, address this need byproposing that the space within the showerhead be partitioned into aplurality of gas chambers, that gas supply pipings be connected to theindividual gas chambers independently of one another and that aprocessing gas of a given type or at a given flow rate be supplied toeach of a plurality of areas within the substrate surface. The artdisclosed in patent reference literatures 1 and 2 makes it possible toimprove the planar uniformity achieved through a substrate etchingprocess by adjusting the gas concentration at the substrate surface inunits of the individual local areas.

The gases used in the actual substrate processing include a plurality oftypes of gases such as a processing gas that directly affects thesubstrate processing, a gas used to control deposition of reactionproducts resulting from the substrate processing and a carrier gas suchas an inert gas selected in a specific combination so as to best suitthe material on the substrate undergoing the processing or the specificprocessing conditions. For this reason, a mass flow controller must beinstalled for purposes of flow rate control in correspondence to each ofthe gas supply pipings connected to the individual gas chambers in theshowerhead, as disclosed in patent reference literature 2.

However, such a structure in the related art, which includes a gassupply system in correspondence to the gas to be supplied from each gaschamber even if the gases used for different purposes may contain acommon gas constituent, necessitates flow rate control to be executedseparately for the gas supplied from each gas chamber. This is bound toresult in a complex piping structure and require complex flow ratecontrol for the individual pipings, necessitating, for instance, a largepiping space and leading to a significant increase in the control onus.

In addition, even if the gases can be supplied through simple controlfrom a plurality of areas within the processing chamber, the desiredlevel of planar uniformity must be assured by ensuring that the controldoes not allow any fluctuation of the flow rate ratio (divided flowratio) of the processing gases supplied from the various positions thatmay occur due to, for instance, a fluctuation of the pressures withwhich the gases are drawn in. In other words, the gas supply must becontrolled without being affected by pressure fluctuations or the like.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention, which has beencompleted by addressing the problems discussed above, is to provide agas supply system with a simple piping structure and the like, withwhich the desired level of planar uniformity is achieved by supplyingthe gases from a plurality of positions within the processing chamberunder simple control.

The object described above is achieved in an aspect of the presentinvention by providing a gas supply system that supplies gases into aprocessing chamber where a substrate undergoing processing is processed,comprising a processing gas supply means for supplying a processing gasto be used to process the substrate, a processing gas supply passagethrough which the processing gas from the processing gas supply meansflows, a first branch passage and a second branch passage branching fromthe processing gas supply passage and connected to the processingchamber at different positions, a divided flow rate adjustment means foradjusting the divided flow rates of the processing gas diverted into theindividual branch passages from the processing gas supply passage basedupon the pressures within the branch passages, an additional gas supplymeans for supplying an additional gas, an additional gas supply passagethrough which the additional gas from the additional gas supply means ismade to flow into the second branch passage at a position furtherdownstream relative to the divided flow rate adjustment means and acontrol means for supplying the processing gas via the processing gassupply means and executing pressure ratio control on the divided flowrate adjustment means to adjust the divided flow rates so as to achievea target pressure ratio for the pressures within the individual branchpassages before processing the substrate and for supplying theadditional gas via the additional gas supply means after switching thecontrol on the divided flow rate adjustment means to steady pressurecontrol through which the divided flow rates are adjusted so as to holdthe pressure in the first branch passage at a level achieved in stablepressure conditions once the pressures in the individual branch passagesbecome stabilized.

The object described above is achieved in another aspect of the presentinvention by providing a substrate processing apparatus comprising aprocessing chamber where a substrate is processed, a gas supply systemthat supplies gases into the processing chamber and a control means forcontrolling the gas supply system. The gas supply system in thesubstrate processing apparatus comprises a processing gas supply meansfor supplying a processing gas to be used to process the substrate, aprocessing gas supply passage through which the processing gas from theprocessing gas supply means flows, a first branch passage and a secondbranch passage branching from the processing gas supply passage andconnected to the processing chamber at different positions, a dividedflow rate adjustment means for adjusting the divided flow rates of theprocessing gas diverted into the individual branch passages from theprocessing gas supply passage based upon the pressures within the branchpassages, an additional gas supply means for supplying an additional gasand an additional gas supply passage through which the additional gasfrom the additional gas supply means is made to flow into the secondbranch passage at a position further downstream relative to the dividedflow rate adjustment means. The control means supplies the processinggas via the processing gas supply means and executes pressure ratiocontrol on the divided flow rate adjustment means to adjust the dividedflow rates so as to achieve a target pressure ratio for the pressureswithin the individual branch passages before processing the substrateand supplies the additional gas via the additional gas supply meansafter switching the control on the divided flow rate adjustment means tosteady pressure control through which the divided flow rates areadjusted so as to hold the pressure in the first branch passage at alevel achieved in stable pressure conditions once the pressures in theindividual branch passages become stabilized.

The object described above is also achieved in yet another aspect of thepresent invention by providing a gas supply method to be adopted inconjunction with a gas supply system that supplies gases into aprocessing chamber where a substrate is processed. The gas supply systemcomprises a processing gas supply means for supplying a processing gasto be used to process the substrate, a processing gas supply passagethrough which the processing gas from the processing gas supply meansflows, a first branch passage and a second branch passage branching fromthe processing gas supply passage and connected to the processingchamber at different positions, a divided flow rate adjustment means foradjusting the divided flow rates of the processing gas diverted into theindividual branch passages from the processing gas supply passage basedupon the pressures within the branch passages, an additional gas supplymeans for supplying an additional gas and an additional gas supplypassage through which the additional gas from the additional gas supplymeans is made to flow into the second branch passage at a positionfurther downstream relative to the divided flow rate adjustment means.The gas supply method includes a step executed before processing thesubstrate, in which the processing gas is supplied via the processinggas supply means and pressure ratio control is executed on the dividedflow rate adjustment means to adjust the divided flow rates so as toachieve a target pressure ratio for the pressures inside the individualbranch passages and a step executed once the pressures within the branchpassages become stabilized through the pressure ratio control in whichthe additional gas is supplied via the additional gas supply means afterswitching the control on the divided flow rate adjustment means tosteady pressure control for adjusting the divided flow rates so as tohold the pressure in the first branch passage at a level achieved instable pressure conditions.

According to the present invention described above, the processing gasfrom the processing gas supply means is diverted into the first andsecond branch passages, the processing gas originating from theprocessing gas supply means is directly supplied into the processingchamber through the first branch passage and the processing gas, the gascomposition and flow rate of which are adjusted by adding the additionalgas, is supplied into the processing chamber through the second branchpassage. This means that a gas constituent common in the processinggases flowing through the individual branch passages is supplied fromthe common processing gas supply means whereas the gas composition andthe flow rate of the processing gas flowing through the second branchpassage are adjusted by adding the additional gas as necessary. Sincethe structure requires the minimum number of pipings and thus simplifiesthe piping structure, the flow rate control, too, can be simplified.

In addition, since the divided flow control on the divided flow rateadjustment means is switched from the pressure ratio control to thesteady pressure control before supplying the additional gas, theprocessing gas that should flow into the second branch passage is notallowed to flow into the first branch passage even if the pressureinside the second branch passage fluctuates when the additional gas issupplied into the second branch passage. As a result, a specific flowrate ratio (divided flow ratio) is sustained for the flows of theprocessing gas diverted into the individual branch passages even as theadditional gas is supplied, allowing the processing gas, the flow ofwhich is divided at a desired flow rate ratio to be delivered todifferent areas of the substrate surface. Thus, the desired level ofplanar uniformity can be achieved.

Once the pressures within the individual branch passages becomestabilized after starting the additional gas supply, the control meansmay designate the pressure ratio of the pressures in the branch passagesdetected in the stable pressure conditions as a new target pressureratio and may switch the control on the divided flow rate adjustmentmeans to pressure ratio control for adjusting the divided flow rates soas to match the pressure ratio of the pressures in the branch passageswith the new target pressure ratio. By reverting the control on thedivided flow rate adjustment means from the steady pressure control tothe pressure ratio control as described above, the pressure ratio of thepressures within the individual branch passages can be held unchangedthrough the pressure ratio control, since the pressures in the branchpassages also fluctuate if the conductance at the gas supply holeschanges and the pressure ratio is thus controlled to remain unchanged.In other words, even if the conductance at the gas supply holes changesover time, the flow rate ratio of the flows of the processing gasdiverted into the individual branch passages can be held steady at thetarget level.

In addition, the divided flow rate adjustment means may include valveseach used to adjust the flow rate of the processing gas flowing throughone of the branch passages and pressure sensors each used to measure thepressure within one of the branch passages. Such a divided flow rateadjustment means is capable of adjusting the flow rate ratio of theflows of the processing gas originating from the processing gas supplypassage by adjusting the degrees of openness of the valves based uponthe pressures detected with the individual pressure sensors.

The processing gas supply means may include a plurality of gas supplysources and may supply into the processing gas supply passage theprocessing gas constituted with a mixed gas achieved by mixing gasesfrom the individual gas supply sources delivered at specific flow rates.In addition, the additional gas supply means may include a plurality ofgas supply sources and may supply into the additional gas supply passagethe additional gas constituted with a mixed gas containing selectedgases among the gases from the various gas supply sources or containinggases delivered from the gas supply sources and mixed at a predeterminedgas flow rate ratio. In this structure, the processing gas constitutedwith a mixed gas containing a plurality of common gas constituents to bedelivered into both branch passages, is supplied from the processing gassupply means and the additional gas is added as necessary to theprocessing gas flowing through the second branch passage so as to adjustits gas composition or its flow rate. As a result, a further reductionis achieved in the number of pipings required in the structure,resulting in an even simpler piping structure.

Furthermore, the first branch passage may be disposed so that theprocessing gas flowing through the passage is supplied toward a centralarea on the substrate surface in the processing chamber and the secondbranch passage may be disposed so that the processing gas flowingthrough the passage is supplied toward a peripheral area of thesubstrate surface. By adopting this positional arrangement, a furtherimprovement can be achieved in the processing uniformity over thecentral area and the peripheral area of the substrate.

The second branch passage may be made up of a plurality of branchpassages branching from the processing gas supply passage so that theadditional gas from the additional gas supply means can be deliveredinto the plurality of second branch passages. In this case, theprocessing gas can be delivered to each of a plurality of areas in theperiphery of the substrate, which enables even finer control forachieving processing uniformity at the peripheral area of the substrate.

The present invention provides a gas supply system assuming a simplepiping structure and the like with which a gas can be supplied from aplurality of positions within the processing chamber under simplecontrol the desired level of planar uniformity can be assured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an example of a structure that may beadopted in a substrate processing apparatus achieved in an embodiment ofthe present invention;

FIG. 2 is a block diagram showing an example of a structure that may beadopted in the control unit in FIG. 1;

FIG. 3 is a block diagram showing an example of a structure that may beadopted in the gas supply system in the embodiment;

FIG. 4 presents a flowchart of an example of processing that may beexecuted in the substrate processing apparatus in the embodiment; and

FIG. 5 presents a flowchart of another example of processing that may beexecuted in the substrate processing apparatus in the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following is a detailed explanation of the preferred embodiment ofthe present invention, given in reference to the attached drawings. Itis to be noted that in the specification and the drawings, the samereference numerals are assigned to components with substantiallyidentical functions and structural features so as to eliminate the needfor a repeated explanation thereof.

(Structural Example for Substrate Processing Apparatus)

First, the substrate processing apparatus achieved in the embodiment ofthe present invention is explained in reference to a drawing. FIG. 1 isa sectional view schematically showing the structure adopted in thesubstrate processing apparatus in the embodiment. The substrateprocessing apparatus in the figure is a plain parallel plate-type plasmaetching apparatus.

The substrate processing apparatus 100 includes a processing chamber 110constituted with a substantially cylindrical processing container. Theprocessing container, which may be constituted of, for instance, analuminum alloy, is electrically grounded. In addition, the inner wallsurfaces of the processing container are coated with an alumina film oran yttrium oxide film.

Inside the processing chamber 110, a susceptor 116 constituting a lowerelectrode also to function as a stage, on which a wafer W, i.e., asubstrate to undergo processing, is placed, is disposed. Morespecifically, the susceptor 116 is supported on a susceptor support base114 assuming the shape of a circular column, which is disposed at asubstantial center at the bottom via an insulating plate 112 within theprocessing chamber 110. The susceptor 116 may be constituted of, forinstance, an aluminum alloy.

Over the susceptor 116, an electrostatic chuck 118, which holds thewafer W, is disposed. The electrostatic chuck 118 includes an internalelectrode 120. A DC power source 122 is electrically connected to theelectrode 120. The wafer W can be attracted and pulled onto the uppersurface of the electromagnetic chuck 118 through the coulomb forcegenerated as a DC voltage is applied to the electrode 120 from the DCpower source 122.

In addition, a focus ring 124 is disposed at the upper surface of thesusceptor 116 so as to enclose the periphery of the electrostatic chuck118. It is to be noted that a cylindrical inner wall member 126constituted of, for instance, quartz, is attached to the outercircumferential surfaces of the susceptor 116 and the susceptor supportbase 114.

A coolant space 128 assuming a ring shape is formed inside the susceptorsupport base 114. The coolant space 128 is made to communicate with achiller unit (not shown), which may be installed, for instance, outsidethe processing chamber 110, via pipings 130 a and 130 b. The coolant (aliquid coolant or cooling water) is supplied via the pipings 130 a and130 b so that the coolant circulates through the coolant space 128. Thetemperature of the wafer W placed on the susceptor 116 is thuscontrolled.

A gas supply line 132 passing through the susceptor 116 and thesusceptor support base 114 is connected to the upper surface of theelectrostatic chuck 118. A heat transfer gas (backside gas) such as Hegas can be delivered to the area between the wafer W and theelectrostatic chuck 118 via this gas supply line 132.

Above the susceptor 116, an upper electrode 134 is disposed so as torange parallel to and face opposite the susceptor 116 constituting thelower electrode. A plasma generation space PS is formed between thesusceptor 116 and the upper electrode 134.

The upper electrode 134 includes an inner upper electrode 138 assuming adisc shape and an outer upper electrode 136 assuming a ring shape andencircling the inner upper electrode 138 from the outside. A dielectricmember 142 assuming a ring shape is disposed between the outer upperelectrode 136 and the inner upper electrode 138. An insulating shield144 assuming a ring shape, which may be constituted of, for instance,alumina, is fitted with a high level of airtightness between the outerupper electrode 136 and the inner circumferential wall of the processingchamber 110.

A first high-frequency power source 154 is electrically connected to theouter upper electrode 136 via a feeder tube 152, a connector 150, anupper feeder rod 148 and a matching unit 146. A high frequency voltagewith a minimum frequency of 40 MHz (e.g., 60 MHz) can be output from thefirst high-frequency power source 154.

The lower end of the feeder tube 152, which may assume a substantiallycylindrical shape with an open bottom, is connected to the outer upperelectrode 136. The lower end of the upper feeder rod 148 is electricallyconnected via the connector 150 to the center of the upper surface ofthe feeder tube 152. The upper end of the upper feeder rod 148 isconnected to the output side of the matching unit 146. The matching unit146, connected to the first high-frequency power source 154, matches theinternal impedance at the first high-frequency power source with a loadimpedance.

The exterior of the feeder tube 152 is covered with a cylindricalgrounded conductor 111 which includes a circular side wall with adiameter substantially equal to the diameter of the processing chamber110. The lower end of the grounded conductor 111 is connected to the topof the side wall of the processing chamber 110. The upper feeder rod 148mentioned earlier passes through the central area of the upper surfaceof the grounded conductor 111, with an insulating member 156 disposedover the area where the grounded conductor 111 and the upper feeder rod148 contact each other.

The inner upper electrode 138 constitutes a showerhead through which aspecific gas is delivered onto the wafer W placed on the susceptor 116.The inner upper electrode 138 includes a round electrode plate 160having formed therein numerous gas supply holes 160 a and an electrodesupport member 162 that detachably supports the upper surface side ofthe electrode plate 160. The electrode support member 162 assumes theshape of a disc with a diameter substantially equal to the diameter ofthe electrode plate 160.

A buffer space 163 constituted with a cylindrical space is formed insidethe electrode support member 162. An annular barrier member 164 isinstalled inside the buffer space 163 and the buffer space 163 isdivided by the annular barrier member 164 into an inner first bufferspace 163 a constituted with a cylindrical space and an outer secondbuffer space 163 b constituted with a ring-shaped space surrounding thefirst buffer space 163 a. This annular barrier member 164 may beconstituted with, for instance, an O-ring.

The first buffer space 163 a is formed so as to face opposite thecentral area (the central portion) of the wafer W placed on thesusceptor 116, whereas the second buffer space 163 b is formed so as toface opposite the peripheral area (edge portion) of the wafer Wsurrounding the central area.

The gas supply holes 160 a communicate with the lower surface rangingover the buffer spaces 163 a and 163 b. Thus, a specific gas can beinjected toward the central portion of the wafer W via the first bufferspace 163 a, whereas the specific gas can be injected toward the edgeportion of the wafer W via the second buffer space 163 b. The specificgas is supplied via a gas supply system 200 into the individual bufferspaces 163 a and 163 b.

A lower feeder tube 170 is electrically connected to the upper surfaceof the electrode support member 162, as shown in FIG. 1. The lowerfeeder tube 170 is connected to the upper feeder rod 148 via theconnector 150. A variable capacitor 172 is installed in the lower feedertube 170. Through adjustment of the electrostatic capacity of thevariable capacitor 172, the relative ratio of the intensity of theelectrical field formed directly under the outer upper electrode 136 andthe intensity of the electrical field formed directly under the innerupper electrode 138 as the high frequency voltage from the firsthigh-frequency power source 154 is applied can be adjusted.

An exhaust port 174 is formed at the bottom of the processing chamber110. The exhaust port 174 is connected via an exhaust pipe 176 to anexhaust device 178 which includes a vacuum pump and the like. As theprocessing chamber 110 is evacuated with the exhaust device 178, thepressure within the processing chamber 110 can be lowered so as toachieve a desired degree of vacuum.

A second high-frequency power source 182 is electrically connected tothe susceptor 116 via a matching unit 180. A high frequency voltage in arange of 2 to 20 MHz, e.g., a high frequency voltage with a frequency of2 MHz, can be output from the second high-frequency power source 182.

A low pass filter 184 is electrically connected to the inner upperelectrode 138 constituting part of the upper electrode 134. The low passfilter 184 is installed so as to block the high-frequency from the firsthigh-frequency power source 154 and pass the high-frequency from thesecond high-frequency power source 182 to the ground. A high pass filter186 is electrically connected to the susceptor 116 constituting thelower electrode. The high pass filter 186 is installed so as to pass thehigh-frequency from the first high-frequency power source 154 to theground.

(Gas Supply System)

Next, the gas supply system 200 is explained in reference to drawings.In the example presented in FIG. 1, the processing gas is divided intotwo flows, i.e., a first processing gas (processing gas for the centerportion) to be delivered toward the central portion of the wafer Winside the processing chamber 110 and a second processing gas(processing gas for the edge portion) to be delivered toward the edgeportion of the wafer W. It is to be noted that instead of dividing theprocessing gas into two separate flows as in the embodiment, theprocessing gas may be divided into three or more separate flows.

As shown in FIG. 1, the gas supply system 200 comprises a processing gassupply means 210 for supplying a processing gas to be used to execute aspecific type of processing on the wafer W, such as film formation oretching, and an additional gas supply means 220 for supplying a specifictype of additional gas. The processing gas supply means 210 is connectedwith a processing gas supply piping 202 constituting a processing gassupply passage, and a first branch piping 204 to constitute a firstbranch passage and a second branch piping 206 to constitute a secondbranch passage both branch out from the processing gas supply piping202. It is to be noted that the first and second branch pipings 204 and206 may branch out inside a divided flow rate adjustment means 230 orthey may branch outside the divided flow rate adjustment means 230.

The first and second branch pipings 204 and 206 are connected to theupper electrode 134 in the processing chamber 110 at differentpositions, e.g., to the first and second buffer spaces 163 a and 163 bin the inner upper electrode 138.

The gas supply system 200 further includes the divided flow rateadjustment means (e.g., a flow splitter) 230 for adjusting the flowrates of the divided processing gas flows, i.e., the first processinggas and the second processing gas, through the first and second branchpipings 204 and 206 based upon the pressures detected within the firstand second branch pipings 204 and 206. In addition, the additional gassupply means 220 is connected to the second branch piping 206 at amiddle position therein via an additional gas supply piping 208 at aposition further downstream relative to the divided flow rate adjustmentmeans 230.

In the gas supply system 200 adopting the structure described above, theprocessing gas originating from the processing gas supply means 210 isdiverted into the first branch piping 204 and the second branch piping206 with the divided flow rates adjusted by the divided flow rateadjustment means 230. The first processing gas flowing through the firstbranch piping 204 is delivered toward the central portion of the wafer Wvia the first buffer space 163 a, whereas the second processing gasflowing through the second branch piping 206 is delivered toward theedge portion of the wafer W via the second buffer space 163 b.

After the additional gas is supplied from the additional gas supplymeans 220 in this gas supply system, the additional gas flows throughthe additional gas supply piping 208 into the second branch piping 206where it is mixed with the second processing gas. Then, the additionalgas, mixed with the second processing gas is delivered toward the edgeportion of the wafer W via the second buffer space 163 b. It is to benoted that a specific example of a structure that may be adopted in thegas supply system 200 is to be described in detail later.

A control unit 300, which controls the various units of the substrateprocessing apparatus 100, is connected to the substrate processingapparatus 100. The control unit 300 controls the DC power source 122,the first high-frequency power source 154, the second high-frequencypower source 182 and the like as well as the processing gas supply means210, the additional gas supply means 220, the divided flow rateadjustment means 230 and the like in the gas supply system 200.

(Structural Example for Control Unit)

An example of a structure that may be adopted in the control unit 300 isnow explained in reference to a drawing. FIG. 2 is a block diagramshowing an example of a structure that may be adopted in the controlunit 300. As shown in FIG. 2, the control unit 300 comprises a CPU(central processing unit) 310 constituting the control unit main body, aRAM (random access memory) 320 that includes a memory area to be used bythe CPU 310 when it executes various types of data processing, a displaymeans 330 constituted with a liquid crystal display or the like at whichan operation screen, a selection screen and the like are displayed, anoperation means 340 constituted with, for instance, a touch panelthrough which the operator is able to input and edit various types ofdata such as process recipes and various types of data including processrecipes and process logs can be output into a specific storage medium, astorage means 350 and an interface 360.

Processing programs that enable the execution of various types ofprocessing in the substrate processing apparatus 100, information (data)needed for the execution of the processing programs and the like arestored in the storage means 350. The storage means 350 may beconstituted with a memory, a hard disk (HDD) or the like. The CPU 310reads out program data and the like as required to execute theprocessing programs for specific types of processing. For instance, theCPU 310 executes gas supply processing by controlling the gas supplysystem 200 so as to supply the specific gas into the processing chamber110 before the wafer W is processed.

The various units controlled by the CPU 310, such as the divided flowrate adjustment means 230, the processing gas supply means 210 and theadditional gas supply means 220, are connected to the interface 360. Theinterface 360 may be constituted with, for instance, a plurality of I/Oports.

The RAM 320, the display means 330, the operation means 340, the storagemeans 350, the interface 360 and the like are connected with the CPU 310via a bus line such as a control bus or a data bus.

(Structural Example for Gas Supply System)

Next, specific structural examples that may be adopted in the individualunits constituting the gas supply system 200 are explained. FIG. 3 is ablock diagram presenting a specific structural example for the gassupply system 200. The processing gas supply means 210 may beconstituted with a gas box housing therein a plurality of (e.g., three)gas supply sources 212 a, 212 b and 212 c, as shown in FIG. 3. Thepipings for the individual gas supply sources 212 a to 212 c areconnected to the processing gas supply piping 202 where the individualgas constituents from the different gas supply sources flow as a mixedgas. At the piping corresponding to each of the gas supply sources 212 ato 212 c, one of mass flow controllers 214 a to 214 c is installed inorder to adjust the flow rate of the specific gas constituent. The gasconstituents from the individual gas supply sources 212 a to 212 c arethus mixed so as to achieve a predetermined flow rate ratio at theprocessing gas supply means 210 adopting the structure described above,and the mixed gas, which then flows out into the processing gas supplypiping 202, is diverted into the first and second branch pipings 204 and206.

The gas supply source 212 a is filled with a C_(x)F_(y) gas, constitutedwith a fluorocarbon fluorine compound such as CF₄, C₄F₆, C₄F₈ or C₅F₈,to be used as, for instance, an etching gas, as shown in FIG. 3. The gassupply source 212 b is filled with O₂ gas, for instance, to be used tocontrol the deposition of, for instance, CF reaction products. The gassupply source 212 c is filled with rare gas such as an Ar gas to be usedas a carrier gas. It is to be noted that the number of gas supplysources at the processing gas supply means 210 is not limited to that inthe example shown in FIG. 3, and there may be a single gas supplysource, two gas supply sources or four or more gas supply sources in theprocessing gas supply means 210.

The additional gas supply means 220 may be constituted with a gas boxhousing therein a plurality of (e.g., two) gas supply sources 222 a and222 b, as shown in FIG. 3. The pipings for the individual gas supplysources 222 a and 222 b are connected to the additional gas supplypiping 208 where the individual gas constituents from the different gassupply sources flow as a mixed gas. At the piping corresponding to eachof the gas supply sources 222 a and 222 b, one of mass flow controllers224 a and 224 b is installed in order to adjust the flow rate of thespecific gas constituent. The gas from either of the gas supply sources222 a and 222 b is selected or the gases from the gas supply sources 222a and 222 b are mixed at a predetermined gas flow rate ratio at theadditional gas supply means 220 adopting the structure described above,and the additional gas from the additional gas supply means, which thenflows out into the additional gas supply piping 208, is delivered intothe second branch piping 206 located further downstream of the dividedflow rate adjustment means 230.

The gas supply source 222 a is filled with a C_(x)F_(y) gas, with whichan etching process, for instance, can be speeded up, whereas the gassupply source 222 b is filled with a O₂ gas with which the depositionof, for instance, CF reaction products can be controlled. It is to benoted that the number of gas supply sources in the additional gas supplymeans 220 is not limited to that in the example presented in FIG. 3, anda single gas supply source or three or more gas supply sources may behoused in the additional gas supply means.

The divided flow rate adjustment means 230 includes a pressureadjustment unit 232 which adjusts the pressure inside the first branchpiping 204 and a pressure adjustment unit 234 that adjusts the pressureinside the second branch piping 206. More specifically, the pressureadjustment unit 232 comprises a pressure sensor 232 a that detects thepressure inside the first branch piping 204 and a valve 232 b via whichthe degree of openness of the first branch piping 204 is adjusted,whereas the pressure adjustment unit 234 comprises a pressure sensor 234a that detects the pressure inside the second branch piping 206 and avalve 234 b via which the degree of openness of the second branch piping206 is adjusted.

The pressure adjustment units 232 and 234 are connected to a pressurecontroller 240 which, in response to a command issued by the controlunit 300, adjusts the degrees of openness of the valves 232 b and 234 bbased upon the pressures detected with the pressure sensors 232 a and234 a respectively. The control unit 300 may control the divided flowrate adjustment means 230 through, for instance, pressure ratio control.In such a case, the pressure controller 240 adjusts the degrees ofopenness of the valves 232 b and 234 b so that the flow rates of thefirst and second processing gases achieve a target flow rate ratioindicated in the command from the control unit 300, i.e., so that thepressures inside the first and second branch pipings 204 and 206 achievea target pressure ratio. It is to be noted that the pressure controller240 may be a control board built into the divided flow rate adjustmentmeans 230, or it may be provided in a separate frame from the dividedflow rate adjustment means 230. As a further alternative, the pressurecontroller 240 may be installed within the control unit 300.

Before the processing on the wafer W, such as etching, a specific gas issupplied into the processing chamber 110 via the gas supply system 200in the substrate processing apparatus 100. More specifically, theprocessing gas is first supplied from the processing gas supply means210 and pressure ratio control is executed for the divided flow rateadjustment means 230. Then, once the pressure ratio of the pressuresinside the first and second branch pipings 204 and 206 is adjusted tothe target pressure ratio, the additional gas from the additional gassupply means 220 is delivered into the second branch piping 206.

The following problem is bound to occur if the additional gas isdelivered into the second branch piping 206 while the divided flow rateadjustment means 230 remains under the pressure ratio control. Namely,as the additional gas is delivered into the second branch piping 206,the pressure inside the second branch piping 206 will rise to a levelhigher than the pressure inside the first branch piping 204, therebyaltering the pressure ratio, and accordingly, the divided flow rateadjustment means 230 will automatically adjust the degrees of opennessof the valves 232 b and 234 b so as to sustain the target pressureratio. As a result, the first processing gas will flow in greaterquantity than the second processing gas, causing the flow rate ratio ofthe flow rates of the first and second processing gases to becomedestabilized due to the additional gas supply.

This problem may be addressed by fixing the degrees of openness of thevalves 232 b and 234 b in the divided flow rate adjustment means 230once the pressure ratio of the pressures inside the first and secondbranch pipings 204 and 206 becomes equal to the target pressure ratioand the pressures inside the individual pipes become stabilized and thenby supplying the additional gas, so as to disallow automatic engagementof the valves 232 b and 234 b when the additional gas is supplied and tohold the flow rate ratio of the first and second processing gasesunchanged.

However, since the pressure inside the second branch piping 206increases as the additional gas is supplied, the processing gas will bediverted toward the second branch piping 206 less readily and moreprocessing gas will be allowed to flow into the first branch piping 204if the settings at the valves 232 b and 234 b in the divided flow rateadjustment means 230 are fixed as described above. In other words, evenif the settings at the valves 232 b and 234 b in the divided flow rateadjustment means 230 are fixed, the flow rate ratio of the flow rates ofthe first and second processing gases will be destabilized as theadditional gas is supplied.

Accordingly, the divided flow control in the divided flow rateadjustment means 230 is switched from the pressure ratio control underwhich the pressures inside the first and second branch pipings 204 and206 are controlled so as to sustain the target pressure ratio, to steadypressure control, under which the pressure inside the first branchpiping 204 is held at a steady level, before the additional gas supplystarts in the gas supply processing according to the present invention.Once the divided flow control is switched, the additional gas supply isstarted.

By adopting these measures, it is ensured that the pressure inside thefirst branch piping 204 is held at a steady level even as the additionalgas is supplied and, as a result, even if the pressure inside the secondbranch piping 206 fluctuates, the processing gas that should be divertedinto the second branch piping 206 is not allowed to flow into the firstbranch piping 204. Thus, the flow rate ratio of the first and secondprocessing gases does not become unstable due to the additional gassupply.

(Example of Gas Supply Processing)

Now, a specific example of the gas supply processing executed in theembodiment of the present invention described above is explained. FIG. 4presents a flowchart of a specific example of processing that may beexecuted in the substrate processing apparatus, which includes the gassupply processing according to the present invention. First, the controlunit 300 starts supplying the processing gas via the processing gassupply means 210 in step S110. A predetermined type of gas within theprocessing gas supply means 210 thus flows into the processing gassupply piping 202 at a predetermined flow rate. More specifically, theC_(x)F_(y) gas, the O₂ gas and the Ar gas supplied from the gas supplysources 212 a to 212 c at predetermined flow rates become mixed, therebyforming a mixed gas containing the C_(x)F_(y) gas, the O₂ gas and the Argas with a predetermined mixing ratio. This mixed gas constituting theprocessing gas then flows into the processing gas supply piping 202.

Then, in step S120, the control unit 300 executes the pressure ratiocontrol for the divided flow rate adjustment means 230, under which thedivided flow rate adjustment means 230 adjusts the flow rates of thedivided flows of the processing gas. More specifically, in response to apressure ratio control command issued by the control unit 300, thedivided flow rate adjustment means 230 adjusts the degrees of opennessof the valves 232 b and 234 b based upon the pressures measured by thepressure sensors 232 a and 234 a under the control executed by thepressure controller 240, until the pressure ratio of the pressuresinside the first and second branch pipings 204 and 206 becomes equal tothe target pressure ratio. The flow rate ratio of the first and secondprocessing gases to be delivered into the first and second buffer spaces163 a and 163 b via the first and second branch pipings 204 and 206 isthus determined.

Then, in step S130, a decision is made as to whether or not thepressures in the first and second branch pipings 204 and 206 havestabilized. If it is decided that the pressures have stabilized, thecontrol unit 300 executes the steady pressure control for the dividedflow rate adjustment means 230 in step S140, under which the dividedflow rate adjustment means 230 adjusts the flow rates of the dividedflows of the processing gas.

Namely, in response to a steady pressure control command issued by thecontrol unit 300, the divided flow rate adjustment means 230 adjusts thedegrees of openness of the valves 232 b and 234 b based upon thepressures measured by the pressure sensors 232 a and 234 a under thecontrol executed by the pressure controller 240, so as to hold steadythe pressure of the first processing gas flowing through the firstbranch piping 204. It is to be noted that the mixed gas (with which thesame etching process can be executed) with the same gas composition asthat of the mixed gas delivered into the first buffer space 163 a, atleast, will also have been delivered into the second buffer space 163 bat this point in time.

In step S150, the control unit 300 starts supplying the additional gasvia the additional gas supply means 220. The predetermined type ofadditional gas is thus delivered at a predetermined flow rate from theadditional gas supply means 220 into the second branch piping 206 viathe additional gas supply piping 208.

In this example, a C_(x)F_(y) gas (e.g., CF₄ gas) with which the etchingprocess can be accelerated is supplied at the predetermined flow ratefrom the gas supply source 222 a via the additional gas supply means 220and the gas delivered from the additional gas supply means is thendiverted into the second branch piping 206 to be supplied into thesecond buffer space 163 b via the second branch piping 206. As a result,a processing gas with a higher CF₄ content compared to the processinggas delivered into the first buffer space 163 a is supplied into thesecond buffer space 163 b. The gas composition and the flow rate of theprocessing gas to be delivered into the second buffer space 163 b aredetermined in this manner.

Then, in step S160, a decision is made as to whether or not thepressures inside the first and second branch pipings 204 and 206 haveboth stabilized. If it is decided in step S160 that the pressures havebecome stable, the processing of the wafer W is executed in step S200.Through the gas supply processing described above, the mixed gas flowingthrough the first buffer space 163 a is delivered over the space nearthe center of the wafer W placed on the susceptor 116 and the mixed gaswith a higher CF₄ gas concentration flowing through the second bufferspace 163 b is delivered to the space over the periphery of the wafer Wunder depressurized conditions in the substrate processing apparatus100. As a result, the etching characteristics at the periphery of thewafer W can be adjusted relative to the etching characteristics at thecentral area of the wafer W, which makes it possible to assure uniformplanar etching characteristics at the wafer W.

Through the processing in the flowchart presented in FIG. 4 explainedabove, the processing gas from the processing gas supply means 210 isdiverted into the first and second branch pipings 204 and 206, theprocessing gas from the processing gas supply means 210 is directlydelivered into the processing chamber 110 via the first branch piping204, and a specific type of additional gases added into the processinggas flowing through the second branch piping 206 so as to deliver theprocessing gas into the processing chamber 110 after adjusting its gascomposition and flow rate. Thus, the processing gas constituted ofcommon gas constituents to flow through both the branch pipings 204 and206 is supplied from the processing gas supply means 210, and theadditional gas is added into the processing gas flowing through thesecond branch piping 206 as necessary so as to adjust its gascomposition or flow rate. This means that when the processing gas isflowing through the individual branch pipings have a large number ofcommon gas constituents, the optimal processing gas supply can beachieved with fewer pipes than that required in a structure thatincludes processing gas sources installed in correspondence to theindividual branch pipings. Since the number of pipes in the gas supplysystem 200 is thus minimized, the piping structure in the gas supplysystem 200 is further simplified. In addition, since the flow rates ofthe divided flows of the processing gas are adjusted based upon thepressures inside the individual branch pipings 204 and 206, theprocessing gas can be supplied through a plurality of positions withinthe processing chamber 110 without requiring complex control.

Furthermore, by simply switching the control on the divided flow rateadjustment means 230 from the pressure ratio control to the steadypressure control prior to the start of the additional gas supply, it isensured that the divided flow rate adjustment means 230 adjusts thevalves 232 b and 234 b so as to hold the pressure in the first branchpiping 204 at a steady level under the steady pressure control even ifthe pressure ratio of the pressures in the first and second branchpipings 204 and 206 fluctuates as the additional gas supply starts. As aresult, the processing gas that should flow into the second branchpiping 206 is not even partially allowed to flow into the first branchpiping 204. Since the flow rate ratio of the first and second processinggases from the divided flow rate adjustment means 230 does not fluctuateas the additional gas supply starts as described above, the desiredlevel of planar uniformity is assured.

It is to be noted that while an explanation is given in reference toFIG. 4 on an example in which the wafer is processed by sustaining thesteady pressure control for the divided flow rate adjustment means 230selected in step S140, the control on the divided flow rate adjustmentmeans 230 may revert to the pressure ratio control prior to the waferprocessing.

For instance, the conductance at the gas supply holes 160 a may changedue to a gradual increase in the temperature at the upper electrode 134while processing a single wafer or while continuously processing aplurality of wafers, and in such a case, the gas may no longer flowsmoothly.

Under such circumstances, the pressures within the first and secondbranch pipings 204 and 206 will both rise and thus, if the steadypressure control for the divided flow rate adjustment means 230 issustained, the valves 232 b and 234 b will be adjusted so as to hold thepressure in the first branch piping 204 alone at a steady level. As aresult, the ratio of the second processing gas flowing into the secondbranch piping 206 will gradually increase relative to the ratio of thefirst processing gas flowing into the first branch piping 204, resultingin destabilization of the flow rate ratio of the first and secondprocessing gases.

This phenomenon may be prevented by reverting to the pressure ratiocontrol prior to the wafer processing. Namely, by reverting to thepressure ratio control, it is ensured that the pressures within thefirst and second branch pipings 204 and 206 will both fluctuate and thepressure ratio will remain unchanged even when the conductance at thegas supply holes 160 a changes. In other words, the divided flow rateadjustment means can be controlled so as to ensure that the pressureratio of the pressures within the first and second branch pipings 204and 206 remains unchanged. By adopting these measures, it is thusensured that any change in the conductance at the gas supply holes 160 aoccurring over time will not alter the flow rate ratio of the first andsecond processing gases.

More specifically, additional processing may be executed in steps S170and S180 prior to the processing in step S200, as shown in FIG. 5.Namely, in the flowchart presented in FIG. 5, the control on the dividedflow rate adjustment means 230 is switched to the pressure ratio controlby the control unit 300 in step S170 if it is decided in step S160 thatthe pressures in the first and second branch pipings 204 and 206 havestabilized. In more specific terms, the pressure ratio is of thepressures inside the first and second branch pipings 204 and 206measured when the pressures have stabilized is designated as a newtarget pressure ratio and the control on the divided flow rateadjustment means 230 is switched to pressure ratio control for adjustingthe flow rates for the divided flows so as to achieve the new targetpressure ratio with the pressures in the first and second branch pipings204 and 206. In the processing, the pressure ratio of the pressuresinside the first and second branch pipings 204 and 206 measured instable pressure conditions is designated as the new target pressureratio for the following reasons; as the additional gas is beingdelivered into the second branch piping 206, the additional gas in thesecond branch pipe alters the pressure inside the second branch piping206 and accordingly, the fluctuation of the pressure attributable to theadditional gas delivered into the second branch piping is taken intoconsideration in the pressure ratio control so as to enable the dividedflow rate adjustment means 230 to adjust the flow rates of the dividedflows without affecting the flow rate ratio of the first and secondprocessing gases.

Then, in step S180, a decision is made as to whether or not thepressures inside the first and second branch pipings 204 and 206 haveboth stabilized. If it is decided in step S180 that the pressures havebecome stable, the processing of the wafer W is executed in step S200.

Through the processing in FIG. 5 explained above, the wafer can beprocessed while preventing fluctuation of the flow rate ratio of thefirst and second processing gases even if the conductance at the gassupply holes 160 a at the upper electrode 134 changes while executingthe wafer processing.

It is to be noted that the second branch piping 206 in the embodimentmay be made up of a plurality of branch pipings branching from theprocessing gas supply piping 202 so that the additional gas from theadditional gas supply means 220 can be delivered into the plurality ofsecond branch pipings. In this case, the processing gas can be deliveredto each of a plurality of areas in the periphery of the wafer, whichenables even finer control for achieving processing uniformity at theperipheral area of the wafer.

In addition, while an explanation is given above in reference to theembodiment on an example in which the processing gas supplied from thegas supply system 200 is injected toward the wafer W through the top ofthe processing chamber 110, the present invention is not limited to thisexample and it may be adopted in conjunction with a structure in whichthe processing gas is also delivered through another portion of theprocessing chamber 110 such as the side surface of the processingchamber 110 facing the plasma generation space PS. Since this will allowthe specific type of processing gas to be delivered from above and theside of the plasma generation space PS, adjustment of the gasconcentration within the plasma generation space PS will be enabled,which, in turn, further improves the planar uniformity of the waferbeing processed.

While the invention has been particularly shown and described withrespect to the preferred embodiment thereof by referring to the attacheddrawings, the present invention is not limited to this example and itwill be understood by those skilled in the art that various changes inform and detail may be made therein without departing from the spirit,scope and teaching of the invention.

For instance, while an explanation is given above in reference to theembodiment on an example in which the flow rates of the divided flow ofthe processing gas diverted into the branch pipings are adjusted via thepressure adjustment units, the present invention is not limited to thisexample and the flow rates of the divided flows of the processing gasdiverted into the branch pipings may instead be adjusted by using massflow controllers. In addition, while an explanation is given above inreference to the embodiment on an example in which the present inventionis adopted in a plasma etching apparatus used to process substrates, thepresent invention may also be adopted in other types of substrateprocessing apparatuses to which processing gases are supplied, e.g.,film forming apparatuses such as a plasma CVD apparatus, a sputteringapparatus and a thermal oxidation apparatus. Furthermore, the presentinvention may be adopted in substrate processing apparatuses in whichsubstrates other than wafers, such as FPDs (flat panel displays) andmask reticles for photomasks, are processed or MEMS (micro-electromechanical system) manufacturing apparatuses, as well.

1. A gas supply system that supplies gases into a processing chamberwhere a substrate is processed, the system comprising: a processing gassupply unit that supplies a processing gas to be used to process thesubstrate; a processing gas supply passage through which the processinggas from the processing gas supply unit flows; a first branch passageand a second branch passage branching from the processing gas supplypassage and connected to the processing chamber at different positions;a divided flow rate adjustment unit that adjusts the divided flow ratesof the processing gas diverted into the branch passages from theprocessing gas supply passage by using mass flow controllers; anadditional gas supply unit that supplies an additional gas; anadditional gas supply passage through which the additional gas from theadditional gas supply unit is made to flow into the second branchpassage at a position further downstream relative to the divided flowrate adjustment unit; a divided flow rate adjustment unit controllerthat switches between a divided flow ratio control which adjusts thedivided flow rates to hold the divided flow ratio in the branch passagesat a target divided flow ratio and a steady pressure control whichadjusts the divided flow rates to hold the pressure in the first branchpassage, and executes each of the controls on the divided flow rateadjustment unit; and a control unit configured to execute a processcomprising: supplying, before processing the substrate, the processinggas by the divided flow rate adjustment unit controller via theprocessing gas supply unit, and executing the divided flow ratio controlon the divided flow rate adjustment unit to adjust the divided flowrates so as to achieve a target divided flow ratio for the divided flowratio in the branch passages; executing, once the pressures in thebranch passages become stabilized through the divided flow ratiocontrol, the steady pressure control by the divided flow rate adjustmentunit controller on the divided flow rate adjustment unit to adjust thedivided flow rates to hold the pressure in the first branch passage at alevel achieved in stable pressure conditions; and supplying theadditional gas via the additional gas supply unit after switching fromthe divided flow ratio control to the steady pressure control.
 2. Thegas supply system according to claim 1, wherein the processing gassupply unit includes a plurality of gas supply sources and supplies intothe processing gas supply passage the processing gas constituted with amixed gas achieved by mixing gases from the gas supply sources deliveredat specific flow rates.
 3. The gas supply system according to claim 1,wherein the additional gas supply unit includes a plurality of gassupply sources and supplies into the additional gas supply passage theadditional gas constituted with a mixed gas containing selected gasesamong the gases from the gas supply sources or containing gasesdelivered from the gas supply sources with a predetermined gas flow rateratio.
 4. The gas supply system according to claim 1, wherein the firstbranch passage is disposed so that the processing gas flowing throughthe first branch passage is supplied toward a central area on a surfaceof the substrate in the processing chamber, and the second branchpassage is disposed so that the processing gas flowing through thesecond branch passage is supplied toward a peripheral area on thesurface of the substrate.
 5. The gas supply system according to claim 1,wherein the second branch passage is made up of a plurality of branchpassages branching from the processing gas supply passage so that theadditional gas from the additional gas supply unit is delivered into theplurality of second branch passages.
 6. A substrate processing apparatuscomprising: a processing chamber where a substrate is processed; aprocessing gas supply unit that supplies a processing gas to be used toprocess the substrate; a processing gas supply passage through which theprocessing gas from the processing gas supply unit flows; a first branchpassage and a second branch passage branching from the processing gassupply passage and connected to the processing chamber at differentpositions; a divided flow rate adjustment unit that adjusts the dividedflow rates of the processing gas diverted into the branch passages fromthe processing gas supply passage by using mass flow controllers; anadditional gas supply unit that supplies an additional gas; anadditional gas supply passage through which the additional gas from theadditional gas supply unit is made to flow into the second branchpassage at a position further downstream relative to the divided flowrate adjustment unit; a divided flow rate adjustment unit controllerthat switches between a divided flow ratio control which adjusts thedivided flow rates to hold the divided flow ratio in the branch passagesat a target divided flow ratio and a steady pressure control whichadjusts the divided flow rates to hold the pressure in the first branchpassage, and executes each of the controls on the divided flow rateadjustment unit; and a control unit configured to execute a processcomprising: supplying, before processing the substrate, the processinggas using the divided flow rate adjustment unit controller and theprocessing gas supply unit; executing the divided flow ratio control,using the divided flow rate adjustment unit controller, on the dividedflow rate adjustment unit to adjust the divided flow rates to achieve atarget divided flow ratio for the divided flow ratio in the branchpassages; executing the steady pressure control, using the divided flowrate adjustment unit controller and once the pressures in the branchpassages become stabilized through the controlling, on the divided flowrate adjustment unit to adjust the divided flow rates to hold thepressure in the first branch passage at a level achieved in stablepressure conditions; and supplying the additional gas via the additionalgas supply unit after switching from the divided flow ratio control tothe steady pressure control.
 7. The substrate processing apparatusaccording to claim 6, wherein the processing gas supply unit includes aplurality of gas supply sources and supplies into the processing gassupply passage the processing gas constituted with a mixed gas achievedby mixing gases from the gas supply sources delivered at specific flowrates.
 8. The substrate processing apparatus according to claim 6,wherein the additional gas supply unit includes a plurality of gassupply sources and supplies into the additional gas supply passage theadditional gas constituted with a mixed gas containing selected gasesamong the gases from the gas supply sources or containing gasesdelivered from the gas supply sources with a predetermined gas flow rateratio.
 9. The substrate processing apparatus according to claim 6,wherein the first branch passage is disposed so that the processing gasflowing through the first branch passage is supplied toward a centralarea on a surface of the substrate in the processing chamber, and thesecond branch passage is disposed so that the processing gas flowingthrough the second branch passage is supplied toward a peripheral areaon the surface of the substrate.
 10. The substrate processing apparatusaccording to claim 6, wherein the second branch passage is made up of aplurality of branch passages branching from the processing gas supplypassage so that the additional gas from the additional gas supply unitis delivered into the plurality of second branch passages.